Last year, a star-studded (RED) auction at Sotheby's in New York raised a record £21m for HIV/Aids programmes in Africa, at a time when the world was braced for economic collapse. And at the beginning of this year, Vladimir Putin, the Russian Prime Minister (and little known painter) sold his canvas for more than 37 million rubles £700,000 – 32 million more than its pre-sale reserve – at a charity auction in St Petersburg.

It is evident that people buy generously at charity art auctions, even as the rest of the world – including the once buoyant art market – is suffering the icy blasts of recession.

A charity auction at Sotheby's on 21 September will tie together a group of artists from South Africa with the British contemporary arts scene and will aim to continue this upbeat trend, hoping to raise more than £500,000 for the Africa Foundation and Ikamva Labantu charities that fund the care of orphaned and vulnerable children in South Africa.

Apart from the exciting work of Young British Artists stalwarts such as Tracey Emin, Marc Quinn and Antony Gormley, the charity auction will showcase South African artists both established (such as Marlene Dumas and William Kentridge) and those who have rarely been exhibited outside of their homeland. It will give buyers an opportunity to give to a good cause and to discover contemporary artists from far-flung regions who would otherwise have little global exposure.

The event will present a patchwork portrait of modern-day Africa, from its rural corners to its people. Included is a photographic work by Pieter Hugo, from Cape Town, who has captured a Nigerian family staring at his camera with the father dressed as Jesus, complete with stigmata; or there is a portrait of a farm in Zimbabwe by Beezy Bailey, the artist brainchild behind the sale.

The auction promises to have lots of highs: a surprise "spectacle" will kick-start the sale; a black and white photo of Nelson Mandela, sparring on a rooftop a year before he was sent to Robben Island, will be sold alongside an "official" picture marking his 90th birthday last year; Annie Lennox and Alison Jackson have pledged to donate works and a collaboration piece, produced by Bailey and the singer, David Bowie, below, has already created a stir. The pair created 50 such canvases together in 1995 but only three have ever been shown, and sold, in public. These multinational offerings will inevitably draw a starry crowd of bidders.

Oliver Barker, the senior international specialist in contemporary art at Sotheby's, and auctioneer for the sale, said: "We expect interest from many prominent contemporary art collectors and philanthropists."

The fact that Northern Trust – a well-conected investment company – is sponsoring the sale will no doubt help to attract the super-wealthy who want to spend responsibly; it is ironic that at a time when most are tightening their belts, top-tier art philanthropists are digging deep..

While the fortunes of auction houses have generally dipped, however temporarily, charity sales such as this one are an exception to the rule: the rich and famous turn out to "do their bit" for a good cause, the profile of artists from other cultures is boosted and the art world is given a fillip in tough times. Everyone wins.

WOW! Thank you very much for finding that infidel! Now if the two of us can put our heads together and somehow find about 20 million or so, we could maybe win the auction for that amazing painting at Sotheby's on September 21st. But, then again, 20 mill could wind being the opening bid!!!!